Why do gyros use tilt head rather than swashplate

"Rod Buck" wrote in message
...
In message , Terry Spragg
writes

An auto gyro is always flown in autorotation, with fixed plade
pitch set for 'gliding'. If you apply torque to an auto rotor,
you do not get lift, you get propelled groundward.

Alas, not true - an autorotating rotor does NOT normally have negative
blade pitch - it has positive pitch of 1-3 degrees, and therefore
generates lift by rotation.

Therefore, if you powered it by a torque from the hub, it would lift off
perfectly well.

It would NOT try to screw it's way into the ground, as it would if the
blade pitch was neggy.


Pitcairn gyros used jumpstart, where the blades are spun up to well
above normal RPM, in zero pitch, then the usual autorotational pitch of
1-3 degrees is applied (either by collective or by delta-three hinges,
which increase the pitch angle when hub torque disappears.)

You must, of course, declutch the hub drive as soon as you increase
pitch and take off - with no tail rotor or other countertorque means,
you'd spin real fine....


The delta-3 hinge is a ferocious beast - once you get above flight rpm,
you MUST take off, there is no way out - bit like lighting those Shuttle
SRB's - it's not a question of whether you go or not, it's just which
direction....

As soon as you declutch the motor, or reduce motor RPM, the hinges
increase the pitch, and off you go.....

The gyro leaps 1-200 ft in the air, and then the prop drive provides
forward motion to start normal autorotational gyro flight - the rotor
pitch is NOT reduced again to do this - it stays at the normal 1-3 deg.


If you apply
power, you are flying a helicopter, which must have some manual
control over pitch if both powered flight and autorotation is to
be possible.

Wrong again, friend.

It's perfectly possible to have a helo with a fixed pitch rotor, set to
the small positive angle for autorotation, and alter lift by changing
engine power, and thus rpm. (You can then use head gimbal as in gyro to
alter pitch cyclically for directional control).

(The rotor rpm would be quite a bit higher than normal for the same
lift)

However, the rotor momentum (flywheel effect) makes the control
extremely sluggish and impractical, compared to collective pitch
control.

However, one safety improvement would be that, as the rotor is always in
the low-angle suitable for autorotation, if the engine quits, a
freewheel device in the rotor drive chain would ensure you entered auto
painlessly.

--
Rod Buck

Rod,

You just answered soooo many of my questions. THANK YOU! Would you mind
if we talked a bit via e-mail?

Again, thanks

Phil Williamson
Oregon City, Or.